Yukon highways officials are defending their road construction practices after concerns were raised about using waste rock from the Minto mine in the reconstruction of a bridge across a stream where salmon spawn. 

Complaints from the Little Salmon Carmacks First Nation have prompted the Yukon Water Board to issue a stop-work order at the Tatchun Creek bridge reconstruction project near Carmacks with a demand for a monitoring program at the site. 

The First Nation fears leaching from the copper mine's waste rock will harm spawning salmon.

Little Salmon Carmacks First Nation Chief Eric Fairclough filed the complaint.

"Nobody called for this material to be used in the construction of the Tatchun Creek bridge or the highways towards Whitehorse at all," he says.

Allan Nixon, assistant deputy minister of Highways and Public Works, says the rock was tested and retested to ensure it wouldn't harm salmon habitat.

"What's bothering a bit about this is this notion we're just running wild in the woods," he says. "We've done our due diligence on this."

He says engineers, geochemists and fisheries biologists all say the Minto waste rock is safe.​

"We knew absolutely we were going to have to ensure there was no issue with it and we did that and continue to do that and demonstrate that beyond any reasonable doubt there is no issue with this rock."​ he says.

The Tatchun Creek bridge is in dire need of replacement since it was nearly washed away during a recent spring flood.

Contractors have a narrow one-month window to work in the creek before Chinook salmon return to spawn.

The government filed a long-term monitoring plan with the Yukon Water Board on Thursday. It expects the stop-work order will be lifted once that plan is approved.